I've done that already but it's still coming up as Postcode / Zip code in the cardholders details section. This is how I've labeled it on the checkout page:
<th><label for="postcode" >Postcode</label></th>
<td><input type="text" name="postcode" id="postcode" value="" /></td>
Also, is there any way to remove the drop downs for 'select language' and 'choose currency' when you first go to the secure payment page. I've got it so that it comes up 'English' and 'Sterling' but wondered if there was a way to remove the option for the others as we don't need them.